CLI — Clear Interrupt Flag

Opcode	Instruction	Op/En	64-bit Mode	Compat/Leg Mode	Description
FA	CLI	NP	Valid	Valid	Clear interrupt flag; interrupts disabled when interrupt flag cleared.

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
NP	NA	NA	NA	NA

Description

If protected-mode virtual interrupts are not enabled, CLI clears the IF flag in the EFLAGS register. No other flags are affected. Clearing the IF flag causes the processor to ignore maskable external interrupts. The IF flag and the CLI and STI instruction have no affect on the generation of exceptions and NMI interrupts.

When protected-mode virtual interrupts are enabled, CPL is 3, and IOPL is less than 3; CLI clears the VIF flag in the EFLAGS register, leaving IF unaffected. Table 3-6 indicates the action of the CLI instruction depending on the processor operating mode and the CPL/IOPL of the running program or procedure.

CLI operation is the same in non-64-bit modes and 64-bit mode.

Table 3-6. Decision Table for CLI Results

PE	VM	IOPL	CPL	PVI	VIP	VME	CLI Result
0	X	X	X	X	X	X	IF = 0
1	0	≥ CPL	X	X	X	X	IF = 0
1	0	< CPL	3	1	X	X	VIF = 0
1	0	< CPL	< 3	X	X	X	GP Fault
1	0	< CPL	X	0	X	X	GP Fault
1	1	3	X	X	X	X	IF = 0
1	1	< 3	X	X	X	1	VIF = 0
1	1	< 3	X	X	X	0	GP Fault

Notes: * X = This setting has no impact.

Operation

IF PE = 0
  THEN
     IF ← 0; (* Reset Interrupt Flag *)
  ELSE
     IF VM = 0;
       THEN
          IF IOPL ≥ CPL
             THEN
               IF ← 0; (* Reset Interrupt Flag *)
          ELSE
             IF ((IOPL < CPL) and (CPL = 3) and (PVI = 1))
               THEN
                  VIF ← 0; (* Reset Virtual Interrupt Flag *)
               ELSE
                  #GP(0);
             FI;
          FI;
       ELSE (* VM = 1 *)
          IF IOPL = 3
             THEN
               IF ← 0; (* Reset Interrupt Flag *)
             ELSE
               IF (IOPL < 3) AND (VME = 1)
                  THEN
                     VIF ← 0; (* Reset Virtual Interrupt Flag *)
                  ELSE
                     #GP(0);
               FI;
          FI;
     FI;
FI;

Flags Affected

If protected-mode virtual interrupts are not enabled, IF is set to 0 if the CPL is equal to or less than the IOPL; otherwise, it is not affected. The other flags in the EFLAGS register are unaffected.

When protected-mode virtual interrupts are enabled, CPL is 3, and IOPL is less than 3; CLI clears the VIF flag in the EFLAGS register, leaving IF unaffected.

Protected Mode Exceptions

#GP(0)	If the CPL is greater (has less privilege) than the IOPL of the current program or procedure.
#UD	If the LOCK prefix is used.

Real-Address Mode Exceptions

#UD	If the LOCK prefix is used.

Virtual-8086 Mode Exceptions

#GP(0)	If the CPL is greater (has less privilege) than the IOPL of the current program or procedure.
#UD	If the LOCK prefix is used.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

#GP(0)	If the CPL is greater (has less privilege) than the IOPL of the current program or procedure.
#UD	If the LOCK prefix is used.